20 LABORATORY MANUAL OF AGRICULTURE 



Place a thermometer in each hole. The thermometers 

 should be lowered into the holes that are two and three feet 

 deep by means of picture wire attached to the thermometer 

 and held at the top by being fastened to a short stick. It is 

 advisable to wrap with paper the bulbs of the thermometers 

 used in taking temperatures at a depth of two and three feet. 

 The paper wrapped around the bulb serves as an insulation, 

 and thus prevents sudden changes in the reading of the ther- 

 mometer. This makes it possible to remove the thermometer 

 from the hole and read it before the reading changes. If 

 wet paper is used in wrapping the bulbs, it should be allowed 

 to dry thoroughly before the thermometers are used. 



Take the temperature of the air four feet above the sur- 

 face of the ground and also of the soil in each field at 

 the depths indicated. Make temperature readings fifteen 

 minutes after the thermometers are placed, and each succeed- 

 ing fifteen minutes for one hour. Record the readings in the 

 accompanying outline. 



Discuss fully the results of the exercise and account 

 as fully as possible for the facts observed. 



QUESTIONS 



1. Why should the slope of the fields be the same upon which the 

 temperature of the soil is taken ? 



2. What effect has the slope of the land upon the temperature of 

 the soil ? 



3. Is the effect of the slope of the land upon the temperature 

 of the soil ever of practical importance ? When ? 



4. Why should not thermometers be used that have the bulbs 

 wrapped in wet paper ? 



5. What effect has growing vegetation upon the temperature 

 of the soil? 



